1. Biomolecular Mass Spectrometry and Proteomics Group, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands, Netherlands Proteomics Centre and Centre for Biomedical Genetics, The Netherlands, and Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands